Although perhaps not strictly “traditional,” it is entirely possible to make pesto without nuts. Leaving the nuts out entirely usually works just fine, though you may need to adjust the proportions of your other ingredients to ensure that you end up with the right consistency. You can also substitute seeds, particularly sunflower seeds or pumpkin seeds, or add breadcrumbs in place of nuts.
Pine nuts are a staple ingredient in traditional basil pesto, adding both a nutty flavor and an adhesive quality. Basic pesto is little more than pine nuts, garlic, grated Parmesan cheese, and fresh basil leaves. There are many types of pesto, however. In Italian, the word “pesto” means, simply, “pounded,” in reference to how the sauce is most frequently made. Ground pine nuts give the finished pesto volume, but they are not required.
Many pesto varieties omit pine nuts. Most contain nuts of some kind — walnuts are a common substitution — but not all do. A pesto without nuts is still a pesto, even if all it contains is basil, oil, and cheese. It is the process and overall flavor that characterizes the spread, not its specific ingredients.
Just the same, a nut-free pesto will have a different consistency, often thin and sometimes a bit runny. If you are hoping to spread the finished pesto without nuts, rather than simply drizzling it over pasta or into a soup, you may need to work with the proportions of your other ingredients. Usually, reducing the oil and increasing the cheese will compensate for the lack of nuts.
Pesto without nuts made in this fashion is often known as pistou. Pistou is a basil-garlic sauce native to the south of France that is often referred to as “French pesto.” The most basic version of this dish is made of only basil, garlic, olive oil, and sea salt. Chefs often add more — tomatoes are common additions, as are various cheeses — but nuts are rare.
It is usually possible to preserve the texture and feel of Italian pesto by replacing nuts with some other similar substance. Sunflower seeds are a common place to start. These seeds are not always suitable for people with nut allergies, but they have a similar consistency to pine nuts and produce a very similar spread-like texture. They are also usually considerably less expensive than pine nuts.
Preparing pesto with pumpkin seeds is another option, though the taste is likely to be quite different. Some cooks also substitute bread crumbs or crushed crackers for nuts. This adds volume, but can dry out the spread if used in excess. Making pesto without nuts is usually a matter of getting the right consistency and taste.